As an approach to the neural substrates of memory, this project examines characteristics and functional roles of structural changes that occur in nerve cells in the forelimb region of rat motor-sensory cortex when they learn to reach into a chamber for food. Prolonged training increases dexterity and, when the innately nonpreferred forepaw is exclusively trained, paw preference for reaching is reversed. Dendritic fields of nerve cells in a motor-sensory cortex region that appears from lesion, electrical stimulation, unit recording and metabolic activity studies to be critically involved in this behavior increase in size with training. This suggests that new synapses are formed as a consequence of learning and by implication that synapse formation may be a basis for long term memory. To further test this hypothesis, we propose to: 1) delineate the pattern of changes across nerve cell types as a partial description of a "memory circuit", 2) determine the temporal sequence of the dendritic field changes for comparison with nerve cell recording studies of behavioral acquisition, 3) determine whether the structural changes persist beyond the training period, as the memory does, 4) ascertain whether training causes above background levels of formation of synapses in the motor-sensory cortex, and 5) determine where and when in the brain synthetic and energy-producing metabolic processes occur during acquisition and stable performance of the task. Results of these studies will provide evidence as to the involvement of synaptogenesis in the memory process and indicate whether learning (training) brings about active synapse formation.